1. Field of the Invention
The present invention is generally directed to a hearing prosthesis, and more particularly, to stochastic stimulation in a hearing prosthesis.
2. Related Art
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person suffers from hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the cochlea, and thus the sensory hair cells therein, are impeded, for example, by damage to the ossicles. Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As a result, individuals suffering from conductive hearing loss typically receive an acoustic hearing aid. Acoustic hearing aids stimulate an individual's cochlea by providing an amplified sound to the cochlea that causes mechanical motion of the cochlear fluid.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. As such, those suffering from some forms of sensorineural hearing loss are thus unable to derive suitable benefit from conventional acoustic hearing aids. As a result, hearing prostheses that deliver electrical stimulation to nerve cells of the recipient's auditory system have been developed to provide the sensations of hearing to persons whom do not derive adequate benefit from conventional hearing aids. Such electrically-stimulating hearing prostheses deliver electrical stimulation to nerve cells of the recipient's auditory system thereby providing the recipient with a hearing percept.
As used herein, the recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion, and parts of the brain used to sense sounds. Electrically-stimulating hearing prostheses include, for example, auditory brain stimulators and Cochlear™ prostheses (commonly referred to as Cochlear™ prosthetic devices, Cochlear™ implants, Cochlear™ devices, and the like; simply “cochlear implants” herein.)
Oftentimes, sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which transduce acoustic signals into nerve impulses. It is for this purpose that cochlear implants have been developed. Cochlear implants provide a recipient with a hearing percept by delivering electrical stimulation signals directly to the auditory nerve cells, thereby bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use an electrode array implanted in the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound.
Both cochlear implants and hearing aids provide a recipient with a hearing percept by stimulating the cochlea of an individual or patient (collectively referred to as recipient herein) with digital stimulation signals. These stimulation signals may be, for example, electrical pulses delivered directly to the cochlea via the electrode assembly of the cochlear implant, or acoustic information delivered indirectly to the cochlea via the outer and middle ear of the recipient from the output transducer of the hearing aid.